Pipe extraction assisted by pre-stressed strand

ABSTRACT

A machine for extracting a ductile pipe. The machine has a vise which can grip the pipe, and a wire clamp. Each of the wire clamp and vise are supported on a carriage which is movable relative to a frame. This enables the vise to grip and pull the ductile pipe. Additionally, a wire strand may be disposed through the pipe from a far end to the end at which the machine is placed. The wire clamp allows the machine to pre-stress the strand to improve the extraction of the ductile pipe.

BACKGROUND

When small diameter pipes need replacement due to a need for capacity increase or because of a lack of pipe integrity, open-trench methods are often used. Apparatus for direct replacement without trenches are growing, as disclosed in U.S. Pat. Nos. 7,128,499 and 10,584,807, both issued to Wentworth, and both of which are fully incorporated by reference herein.

Direct extraction and replacement of a host pipe offers two major benefits for both the owner of the pipeline and the public. Firstly, the method places the new pipe on the exact path of the existing host pipeline thereby staying within the pipeline right-of-way as required, as well as increasing the likelihood of avoiding damage to adjacent closely spaced utilities that may be parallel in path or cross the path of the host pipe.

There are two known ways to extract small diameter pipes. First, one may use the tensile strength of the existing pipe alone to break the shear strength between the pipe's outer wall and the surrounding soil, thereby allowing said pipe extraction by pulling from one end of the pipe. Alternatively, a strand, such as a high strength wire rope, may be passed through the inside diameter of the pipe with an obstruction, or “pipe puller” at the far end. When the strand is pulled from the opposite end, the pipe may be removed due to the tension supplied by the strand. A combination of these methods may also be used.

Both methods complete the installation by pulling a replacement pipe into the volume previously occupied by the host pipe; either by attaching the replacement pipe to the tail end of the host pipe or the tail end of the strand, or by making a second pull using an additional length of strand to pull on after the host pipe has been removed from the bore.

Pulling the pipe depends solely on pipe tensile strength. As a result, the magnitude of the force that can be applied to extract the pipe is limited exactly to the host pipe tensile strength. Each added foot of host pipe length added to the extraction length adds to the force required to break the shear bond from pipe to soil which limits the lengths of the extraction that can be achieved.

For this reason, a wire rope may be used in some applications. The strength of the strand adds to the length of pipe that can be extracted. Even with the improved distance the strand achieves, it may be advantageous to increase the length of pipe that can be extracted yet more.

The maximum magnitude of extraction force occurs during, the initial pulling cycle, when the pipe outer wall is still adhered to the surrounding soil. Once this adhering bond and its associated static friction has been broken, the extraction or pulling force drops considerably, in the range of 50 to 75%. It is during this initial pulling cycle that the pipes manufactured from low strength materials such as lead are most likely to fail before the pipe soil bond has broken. If the pipe is used without a strand, a broken pipe will cause the extraction to be unsuccessful. Thus, the strand enhances the pipe extraction operation, especially during this initial pulling cycle.

Pipes manufactured from lower strength materials such as lead may have tensile strength of less than ½ of a ton. Steel wire rope in a 5/16″ diameter can have a tensile strength as great as 7 tons. High strength strands can add a substantial extraction force, especially with low strength or small diameter pipes.

While the steel pipe does not elastically stretch a significant amount after long term placement, wound wire rope strands do stretch. When the two components are loaded in parallel in a tensile manner, the differences in the stretch rates affect the magnitude of the load achieved during extraction.

The success or failure of the extraction process is largely a function of the tensile or extraction forces that can be applied to the host pipe. Thus, it is desirable to increase the available extraction force to enable extraction of low strength pipe.

SUMMARY

In one aspect, the invention is directed to a pipe extraction machine. The pipe extraction machine comprises a frame, a carriage, an actuator, a wire clamp, and a pipe cutter. The carriage is movable along, the frame. The carriage comprises a vise. The vise comprises a pair of jaws configured to engage a ductile pipe having a strand extending therethrough. The actuator is connected to the frame and the carriage or moving the vise along the frame between first and second positions. The wire clamp is supported on the carriage and has a plurality of wire jaws. The wire jaws are disposed about a central opening and configured to selectively engage a strand.

In another aspect, the invention is directed to a pipe extraction machine. The pipe extraction machine comprises a frame, a carriage and an actuator. The carriage comprises a pipe vise and a wire clamp. The pipe vise and wire clamp define an axis disposed therethrough. The actuator moves the carriage along the frame. The pipe vise and the wire clamp are each configured to selectively and individually grip a system defining a pipe with an internally disposed wire.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagrammatic representation of a pre-stressing operation. A strand is placed in an existing pipe. Two clamps are disposed about the strand. The machine which pulls the pipe and the strand is removed. In FIG. 1A, the clamps are shown prior to a wire-stressing stroke.

FIG. 1B is a diagrammatic representation of the pre-stressing operation of FIG. 1A. In FIG. 1B, the clamps are shown after a wire-stressing stroke.

FIG. 2 is a side plan view of a strand clamp assembly for use in the operation of FIGS. 1A-1B.

FIG. 3 is a sectional view of the clamp assembly of FIG. 2 along section line A-A.

FIG. 4 is an exploded perspective view of the clamp assembly of FIG. 2.

FIG. 5 is a top view of a pipe pulling assembly having a movable carriage within a support frame.

FIG. 6 is a left side view of the pipe pulling assembly of FIG. 5.

FIG. 7 is a back view of the pipe pulling assembly of FIG. 5, with an opening for accepting a pipe and strand visible.

FIG. 8 is a rear right top perspective view of the pipe pulling assembly of FIGS. 5-7.

FIG. 9 is a cutaway side view of the pipe pulling assembly of FIG. 5, engaged in a wire-stressing operation. In FIG. 9, a wire is secured in a first wire clamp in a first position.

FIG. 10 shows the view of FIG. 9, with the carriage advanced such that the strand has been pulled to the right. A second wire clamp is held in place by the support frame.

FIG. 11 shows the view of FIG. 9, with the first wire clamp moved back for a second stroke, and a pipe clamp surrounding a pipe. The strand is held in tension by the second wire clamp.

FIG. 12 shows the view of FIG. 9, with the carriage advanced such that the pipe and the strand have been pulled to the right. The second wire clamp is released by the support frame to maintain tension on the strand.

FIG. 13 shows a first embodiment of a product pipe puller apparatus.

FIG. 14 is a sectional view of the pipe puller apparatus of FIG. 13 along line C-C.

FIG. 15 is a second embodiment of a pipe puller apparatus.

FIG. 16 is a sectional view of the pipe puller apparatus of FIG. 15 along line D-D.

DETAILED DESCRIPTION

With reference now to FIGS. 1A and 1B, a system 10 which enables the extraction of a pipe is shown. The system 10 will be disposed at two sides of a buried underground pipe 11. The pipe 11 is disposed in an underground environment 200. Often, each side of the pipe 11 will have a pit 202 excavated such that materials, such as pipe extractor 100 (FIGS. 5-8) and other tooling, may be properly placed. Alternatively, one or both exit points may be within a basement, or at the surface of the ground.

The system 10 comprises a buried pipe 11 with first end 11A and second end 11B. A strand 16, such as a wire rope, is disposed inside of the pipe 11 and extends from its first end 11A to the second end 11B. The strand 16 is attached to a pipe puller 13 at the first end 11A. The pipe puller 13 has a larger effective diameter than the first end 11A of the pipe 11 and bears against its face. The pipe puller 13 facilitates attachment between the strand 16 and a replacement pipe 12. The replacement pipe 12 may be made of a flexible and strong material such as high density polyethylene (HDPE). By pulling the replacement pipe 12 as the buried pipe 11 is extracted, the replacement pipe will closely align with the path of the extracted, buried pipe.

The system 10 further comprises a stationary strand clamp 14 and a moving strand clamp 15. The strand clamps 14, 15 may be identical in structure. The strand clamps 14, 15, as shown best in FIGS. 2-4, comprise a nut collar 31, a body 32, and internal jaws 35. The nut collar 31 is selectively positionable within the body 32. As shown, the nut collar 31 has external threads 37 which mate with lands 38 within the body to enable the selective positioning of the nut collar 31. The body 32 comprises an internal passage 34 which cooperates with an internal passage 36 in the nut collar to allow the strand 16 to pass through, as shown in FIGS. 1A-1B.

The internal jaws 35 are capable of at least two configurations, determined by the position of the nut collar 31. When the nut collar 31 is not fully threaded into the body 32, the jaws are unsecured within the strand clamp 14. In this first configuration, a strand 16 (FIGS. 1A-1B) that is disposed within the internal passage 34 of the body, and thus the strand 16 disposed within the jaw aperture 39 (FIG. 4) will not be gripped by the internal jaws 35. A strand clamp 14, 15 in this configuration can freely slide relative to an internally-disposed strand.

When the nut collar 31 is threaded into the body 32, the internal jaws 35 are pressed into the tapered internal surface of the internal passage 34 of the body. This causes the jaw aperture 39 to contract, allowing the surface of each internal jaw 35 to grip or bite an internally disposed strand 16. In this second configuration, a strand clamp 14, 15 will not move relative to the strand 16. The internally-disposed surface of each internal jaw 35 may have features which enhance the gripping function of the strand clamp 14, 15 when in the second configuration, while preventing obstruction when in the first configuration. Threads or similar surface features are possible examples.

When the nut collar 31 is loosened or removed from the body 32, the associated strand clamp 14, 15 moves from the second configuration to the first configuration, again allowing the strand 16 to pass freely within. The taper angle of the internal passage 34 causes the internal jaws 35 to largely be self-initiating when moved in a direction d as shown in FIG. 3, with minimal force required from the nut collar 31 to achieve the second configuration.

As shown, the internal passage 34 has a portion which is complementary to the surface of a conical frustum. Likewise, the external surfaces of the internal jaws are substantially congruent to the surface of a cone, such that force applied by the nut collar 31 at the larger opening of the internal passage 34 forces the jaws 35 closer together. Such movement causes the jaws to place the strand clamp 14, 15 to be placed in the second configuration, configured to grip an internally-disposed strand 16.

With reference again to FIGS. 1A and 1B, the system 10 is shown in two different states. In FIG. 1A, the movable strand clamp 15 is in the second configuration, gripping the strand 16. The stationary strand clamp 14 is in the first configuration and is not gripping the strand. Prior to a stroke of the movable strand clamp 15, the distance between the rear face 33 of the movable strand clamp 15 and the first end 11A of the buried pipe 11 is D.

In FIG. 1B, the movable strand clamp 15 has pulled to the right, stretching the strand 16 by a distance S. If further strokes are required to achieve the desired tension in the strand, the stationary strand clamp 14 may be placed in the second configuration to hold the strand 16 in tension. The movable strand clamp 15 is placed in the first configuration and moved back to the position shown in FIG. 11A. The movable strand clamp 15 is then placed in the second configuration and the process repeated.

Using this method, the extraction force achieved in a subsequent pulling stroke of the pipe can exceed previous methods. With the wire rope restrained under high tensile load, achieved by the stretching step described above, the pipe will be left under an equivalent compressive load. The second end 11B of the pipe can be clamped and the summation of the compressive load on the pipe and the tensile strength of the pipe can be applied to the pipe before either the pipe yields or the rope breaks.

This system 10 thus provides a dual load path which enhances known methods of extracting pipe. The tension on the strand 16 should be held until the first pipe extraction stroke, as described below, is complete and the pipe has been broken loose from the surrounding soil. Typically, required pulling force will drop 50 to 75% after the first extraction pulling cycle, and the pipe alone can withstand the continued (but lower) extraction forces using the methods discussed in U.S. Pat. Nos. 7,128,499 and 10,584,807.

While the functions of pre-stressing the strand and performing the subsequent pipe extraction may be performed by separate apparatus, a pipe extractor 100 capable of both operations is shown in FIGS. 5-8. The pipe extractor 100 comprises a stationary hull or support structure 101 and a movable carriage 102. The carriage 102 is supported on the support structure 101 on rails 105, which allow the carriage to move along a single axis which is parallel to a central opening 108 in the pipe extractor 100.

One or more hydraulic cylinders 103 are shown for moving the carriage 102. While cylinders 103 are shown, other linear actuators may be used to move the carriage, such as a rack and pinion drive.

A face 106 of the support structure 101 may preferably be placed against the soil next to the extraction location for the pipe 11 (FIGS. 1A-1B) and anchored there.

The carriage 102 comprises a pipe clamp or vise 116, which, as described in the incorporated references, may include a pair of opposed jaws having parallel faces, which are forced together in opposite directions by a cam plate to maintain each of the first and second jaw in a parallel arrangement, as described in U.S. Pat. No. 10,584,807, which was previously incorporated by reference. Alternatively, the vise 116 may have two jaws which pivot relative to one another and are actuated together by a cylinder, as described in U.S. Pat. No. 7,128,499.

The carriage 102 further comprises a pipe shear 104, which may shear a length of pipe 11 and strand 16 after it has been removed from its underground location.

With reference to FIGS. 9-12, the system 10 is shown with a pipe extractor 100 included. In the view of FIGS. 9-12, the pipe 11 length is shortened for visibility purposes. Further, it should be understood that the pipe 11 is under a surface of the ground 200, as shown in FIGS. 1A-1B.

The strand 16 is disposed within the pipe n and connected to a pipe puller 13. The pipe puller 13 is connected to a product pipe 12 and bears against the first end 11A of the pipe 11. The pipe 11 is disposed through the central opening 108 (FIG. 7) of the pipe extractor 100.

The pipe extractor 100 further comprises a first pocket in attached to a rear face 109 of the support structure 101. The first pocket 111 is adapted to support and hold the stationary strand clamp 14 in place. The carriage 102 further comprises a second pocket no. The second pocket no is configured to support and hold the movable strand clamp 15 in place. The second pocket no may be disposed within the pipe shear 104 or may be between the pipe shear 104 and the vise 116.

The strand clamps 14, 15 may be secured about the strand 16 by their respective pockets 111, 110. The clamps 14, 15 may be threaded on to the strand 16 by placing the second pocket 110, movable strand clamp 15, second pocket 111 and stationary strand clamp 14 over the end 113 of the strand, in that order. With each element secured in place, the wire rope end 113 may be placed on a spool (not shown) to take in slack as the pulling operation continues.

In FIG. 9, the second end 11B of the pipe 11 is within the vise 116 but the vise 116 is not closed. Movable pipe clamp 15 is placed into the second configuration by tightening the nut collar 31 (FIGS. 1A-4). In FIG. 10, the cylinders 103 actuate to pull the carriage 102, and consequently the strand 16, towards the rear face 109. The pipe 11 is not gripped and therefore remains in place. This step may be repeated until the strand 16 is at a desired tension. Tension is held during the return stroke by placing the stationary strand clamp 14 in its second configuration. The movable strand clamp 15 is placed in its first configuration, and the cylinders 103 retract to move the carriage 102 towards the face 106.

When the desired tension in the strand is achieved, the vise 116 may be actuated about the second end 11B of the pipe 11, as shown in FIG. 11. The movable strand clamp 15 is placed in the second configuration. The second end 11B is clamped or crushed, and the cylinders 103 move the carriage towards rear face 109. As shown in FIG. 12, the pipe 11 is dislodged from its position, breaking adhesion between the pipe 11 and the underground environment in which it is situated. As shown, the pipe puller 13 pulls replacement pipe 12 behind it.

During each stroke of the cylinders 103 to pull the strand and/or the pipe 11, the stationary rope clamp 14 may be in the first configuration, such that the strand will pass unencumbered, or in the second configuration, such that the stationary rope clamp 14 will travel with the strand 16, as shown in FIG. 12.

If further strokes are desired with the rope in tension, the pipe extractor 100 may be placed back in the configuration shown in FIG. 9, with tension held by the stationary pipe clamp 14 during the return stroke of the cylinders. As discussed above, the vise 116 alone may be suitable for subsequent steps after adhesion between the underground environment and the pipe 11 is broken.

Optionally, at this point the pipe 11 and strand 16 may be sheared by pipe shear 104. If the strand 16 is sheared, the pipe puller 13 must be attached to the first end 11A of the pipe such that the installation of the product pipe 12 can continue in subsequent pipe-thrusting steps.

With reference to FIGS. 13-16, embodiments of the pipe puller 13 are shown. As shown in FIGS. 1A-1B and 9-12, the pipe puller 13 is disposed against the first end 11A of the pipe and applies extraction load to the pipe. The puller 13 comprises a pilot nose 26, an expander body 21, a swivel 24 and a carrot puller 23.

The pilot nose 26 may include self-tapping threads 117 (FIGS. 15-16) which facilitate attachment with the pipe 11. Rotation may be applied to the nose 26, and thus the threads 117, through flats 118 (FIG. 15).

The pipe puller 13 has an internally disposed channel 28 within the expander body 21 and pilot nose 26, within which cable jaws 32 are situated. The jaws 32 are secured to the strand 16 (FIGS. 1A-1B, 9-12) by tightening nut 22, which attaches to the internal portion of the expander body 21 with internally disposed threads 29.

The expander body 21 is proximate the nose 26. The expander body 21 has a tapered outer surface, so that soil is expanded away from the bore left by host pipe 11. Expanding the borehole facilitates installation of the replacement pipe 12.

The expander body 21 is attached to the carrot puller 23 by a swivel joint 24. The swivel joint 24 enables the carrot puller 23 to deflect from the host pipe centerline while being installed. The swivel joint 24 allows the pipe puller 13 to better follow the same path as the pipe 11 as replacement pipe 12 is installed and prevents twisting damage to the product replacement pipe 12 as it is installed.

The carrot puller 23 may be of any type typically used in underground utility installation. As shown, the carrot puller 23 cuts threads with cutting features 25, 27 into the inside surface of the product replacement pipe 12 as it is rotated. After installation of puller 23 into product replacement pipe 12, swivel joint 24 may be installed thereby attaching the product replacement pipe 12 to the strand 16.

The replacement pipe 12 is pulled in with the pipe puller 13 as described, or a second length of strand 16 may alternatively be pulled behind the existing pipe 11. The second length of strand may then be used to pull a replacement pipe 12 into the now-empty path of the pipe 11.

Changes may be made in the construction, operation and arrangement of the various parts, elements, steps and procedures described herein without departing from the spirit and scope of the invention as described herein. 

The invention claimed is:
 1. A pipe extraction apparatus comprising: a support structure; a carriage comprising: a vise assembly having a first jaw and a second jaw in face-to-face orientation; a first wire clamp assembly supported on the carriage, the first wire clamp assembly comprising a first plurality of wire jaws disposed about a central passage; and a second wire clamp assembly comprising a second plurality of wire jaws disposed about a central passage; an actuator configured to move the carriage relative to the support structure; wherein each of the first wire clamp assembly and the second wire clamp assembly is capable of a selected one of at least two configurations, in which the central passage has a smaller effective diameter when each of the first and second wire clamp assemblies is in a second configuration of the at least two configurations than when that wire clamp assembly is in a first configuration of the at least two configurations; and wherein at least a portion of the support structure is interposed between the carriage and the second wire clamp assembly.
 2. The pipe extraction apparatus of claim 1 in which the plurality of wire jaws of each of the first and second wire clamp assemblies comprises three jaws.
 3. A system comprising: the pipe extraction apparatus of claim 1; a pipe having a first end within the pipe extraction apparatus, wherein at least a length of the pipe is in an underground environment; and a wire disposed within the pipe, the first wire clamp assembly, and the second wire clamp assembly.
 4. The system of claim 3 further comprising: a pipe puller disposed at a second end of the pipe; and a replacement pipe attached to the pipe puller.
 5. The pipe extraction apparatus of claim 1 in which the vise assembly further comprises: an actuator to move the first jaw in a first direction and to move the second jaw in a second direction while maintaining the first jaw and the second jaw in face-to-face orientation, wherein the first and second directions are directly opposite each other and wherein the actuator comprises a first cylinder oriented no more than 45 degrees from vertical.
 6. The pipe extraction apparatus of claim 1 in which each of the first and second wire clamp assemblies further comprise: a body with a first end and a second end and an internal tapered cavity, wherein the internal tapered cavity has a smaller diameter at its first end than at its second; and a nut collar disposed at the second end of the body and engaging the plurality of wire jaws; wherein the nut collar is configured to selectively position the plurality of wire jaws in one of the first configuration and second configuration.
 7. A method of using the pipe extraction apparatus of claim 1, comprising: disposing a wire strand through an existing pipe, the existing pipe having first and second ends and an underground section disposed between the first and second ends; securing the wire strand to a pipe puller at the second end of the existing pipe; in a first operational step placing the first wire clamp assembly about the wire strand in the second configuration at the first end of the existing pipe; while the first wire clamp assembly is in the second configuration, moving the carriage away from the first end of the existing pipe with the actuator; after the step of moving the carriage away from the first end of the existing pipe, securing the wire strand with the second wire clamp assembly; thereafter, placing the first wire clamp assembly in the first configuration; with the first wire clamp assembly in the first configuration, moving the carriage with the actuator towards the first end of the existing pipe; thereafter, in a second operational step placing the first wire clamp assembly in the second configuration; and with the first wire clamp assembly in the second configuration during the second operational step, moving the carriage away from the first end of the existing pipe with the actuator.
 8. The method of claim 7, further comprising: after the step of placing the first wire clamp assembly about the wire strand in the second configuration and before the step of moving the carriage away from the first end of the existing pipe, closing the vise assembly about the existing pipe.
 9. The method of claim 8 further comprising: after the step of moving the carriage away from the first end of the existing pipe, moving the carriage toward the second end of the existing pipe; and shearing a section of the existing pipe.
 10. The method of claim 7 further comprising: securing a replacement pipe to the pipe puller; and thereafter, extracting the existing pipe and thereby installing the replacement pipe along substantially the same path previously defined by the existing pipe prior to its extraction.
 11. The method of claim 10 in which the pipe puller comprises a frustoconical expander cone.
 12. A pipe extraction machine comprising: a frame; a carriage movable along the frame comprising: a vise comprising a pair of jaws configured to engage a ductile pipe having a strand extending therethrough; an actuator connected to the frame and the carriage for moving the vise along the frame between first and second positions; a pipe cutter; and a first wire clamp supported on the carriage and having a plurality of wire jaws disposed around a central opening, the wire jaws configured to selectively engage the strand; a second wire clamp spaced apart from the carriage and having a plurality of wire jaws disposed around a central opening, the wire jaws configured to selectively engage the strand; in which the second wire clamp is configured to be maintained in position by the frame.
 13. The pipe extraction machine of claim 12 wherein the first wire clamp comprises: a body having a tapered inner passage, wherein the tapered inner passage has a smaller diameter at its first end than at its second end; the plurality of wire jaws, wherein each wire jaw has an outer surface which is congruent to the surface of a cone; and a threaded collar disposed at the second end of the body and engaging the plurality of wire jaws such that the position of the threaded collar determines whether the plurality of wire jaws engage the strand.
 14. A system, comprising: a ductile pipe having the strand extending therethrough; the pipe extraction machine of claim 12; wherein the pair of jaws of the vise are positioned on opposing sides of the ductile pipe; and wherein the strand is disposed within the central opening of the first and second wire clamp.
 15. The system of claim 14 further comprising: a pipe puller attached to the ductile pipe; wherein an entire length of the ductile pipe is disposed about the strand between the pipe puller and the first wire clamp.
 16. The system of claim 15 in which the pipe puller comprises a conical expander body.
 17. The system of claim 15 in which the strand is characterized as a first strand and in which the pipe puller comprises a second strand.
 18. A pipe extraction machine, comprising: a frame comprising a face; a carriage comprising: a pipe vise; and a first wire clamp; wherein the pipe vise and first wire clamp define an axis disposed therethrough; and an actuator for moving the carriage along the frame such that the distance between the carriage and the face changes; a second wire clamp supported on the frame and configured to grip an internally disposed wire when engaged with the face; wherein the pipe vise, the first wire clamp, and the second wire clamp are each configured to selectively and individually grip a system defining a pipe with the internally disposed wire. 